Francisco J. Martínez-Boza

Influence of the processing conditions on the rheological behaviour of polymer-modified bitumen☆☆

Abstract Mixing polymers into bitumen has important consequences on the engineering properties of bituminous binders. Thus, structural and chemical changes may be observed during processing of polymer-modified bitumens. Chemical compatibility and processing conditions are crucial to obtain suitable properties. Most polymers occur to be insoluble, in some degree, in the bitumen matrix, and phase separation may result. Polymer stabilization can be achieved by mechanical dispersion of the modifier and swelling by compatible components in the maltene fraction. This paper deals with the influences that processing variables exert on the rheological properties of polymer-modified bitumens. From the experimental results obtained we may conclude that a rotor–stator mixer device enhances the rheological properties of binders prepared with high-density polyethylene, low-density polyethylene, ethylene–propylene–diene monomer, and their blends, as compared to a stirred tank device.

Rheological characterisation of synthetic binders and unmodified bitumens

Abstract This paper deals with the characterisation of the linear viscoelastic and steady-state flow properties of commercial pigmentable synthetic binders and unmodified bitumens. From the experimental results obtained, we may conclude that both types of materials show a thermorheologically simple linear viscoelastic behaviour in the temperature range studied (5°C–50°C), although synthetic binders are thermorheologically complex materials in steady-state flow. Both of them display a predominant viscous behaviour within the linear viscoelasticity region. Synthetic binders are characterised by an apparent shift of the terminal zone of the relaxation spectrum to lower frequencies, probably related to the development of entanglements among macromolecule components, and by the highest values of the zero-shear-rate limiting viscosity.

Steady-state flow behaviour of synthetic binders

This paper deals with the influences that mineral oil, resin and polymer concentrations, and temperature, exert on the steady-state viscous flow of model synthetic binders. With this aim, both binary (oil/resin and oil/polymer) and ternary systems have been studied. All the systems show a Newtonian region in a shear rate range that depends on binder concentration and temperature. The temperature dependence of the zero-shear-rate-limiting viscosity is described by an Arrhenius-like equation, in a temperature range that depends on binder composition. This limiting viscosity, at any concentration and temperature within the experimental range studied, can be estimated from the values of activation energies and viscosities of the binary oil/resin systems and the polymer concentration used. These results have been discussed on the basis of the development, depending on the polymer/resin ratio, of both a polymer-rich phase and a resin-rich phase in the bulk binder and its influence on the microstructure of the system.

Structure—property relationships in the development of bituminous foams from MDI based prepolymers

Stable bituminous foams based on diphenyl methane-4,4′ diisocyanate (MDI–isocyanate prepolymers) that combine bituminous membranes and polyurethane foams into one material are promising new materials. They are produced in a two-step process: firstly, a reactive modified bitumen is obtained by mixing a bitumen and a prepolymer, and, secondly, a bituminous foam is formed by a reaction of an excess of water with the remaining isocyanate groups. The prepolymer was formed from a polypropylene glycol (PPG) polymer of a molecular weight of about 2,000 g/mol and MDI. The main goal of this study was to investigate the effect that both free MDI (not bonded to the PPG) and polyol (soft segment) exert on the thermorheological behaviour of bituminous polyurethane materials. The results obtained show that free MDI molecules are mostly responsible of the improvement of the viscoelastic and viscous response at high in-service temperatures due to the chemical reaction that give rise to rigid polyurethane and polyurea rigid blocks. PPG molecules partially inhibit the abovementioned effect but improve the low-temperature properties (lower glass transition temperatures). In general, for the used polyol, a good balance of rigidity and flexibility can be obtained if enough amount of a prepolymer containing a molar ratio of MDI/PPG of 5 is used.